Hey Pika,
Since Prism Launcher is a fork of MultiMC, the installation steps are the same for both:
Create a new vanilla instance with the Minecraft version you want to use. I'll use 1.21 in this example.
Click on "Edit instance", then "Install Fabric".
It will ask you which Fabric Loader version to use. The default is fine. Click OK.
Switch to the Loader mods tab.
Add Wurst and the Fabric API here. You can either press the Add button and navigate to where you've saved the files, or just drag and drop them into this window. Once you're done, you'll see both mods listed like this:
Important: Double-check that both Wurst and Fabric API are meant for the Minecraft version you are using (1.21 in this example). The game won't launch if you mix different Minecraft versions.
And that's all there is to it. You now have a working MultiMC / Prism instance for the Wurst Client.
Hope this helps! Let me know if you have any further questions or run into any issues.
